CTV designer says sorry

The engineer who designed the Canterbury Television (CTV) building has called its collapse a "worst-nightmare scenario" and apologised for any mistakes he made.

David Harding, who worked for Alan Reay Consultants in the 1980s, used his final appearance before the Canterbury earthquakes royal commission today to say sorry to the family and friends of the 115 people who died in the building.

"I've spent a lot of time thinking about what to say and what the right time was and I think it got more and more difficult as time went on," he said.

"It's sort of a worst-nightmare scenario for an engineer. All I can do is offer my heartfelt condolences and sympathy ... and to apologise for any contribution to that failure which was caused by anything I should or shouldn't have done.

"I won't be forgetting this."

Harding said the building was designed to best-practice standards in most areas, and the sheer force of the earthquake on February 22 last year triggered its collapse.

"I really do think it was the vertical acceleration which the [building] code didn't make provision for."

He admitted that spiral steel reinforcing in the building's columns was too widely spaced and that concrete columns in the building had not been designed to bend and absorb the shaking forces of an earthquake, but said this had no effect on its fate.

"[The columns] couldn't be expected to take that load even if they had been detailed for ductility,'' he said.

"I've obviously given it a lot of thought and a lot of sleepless nights about what I could have done differently and I believe that there were a few details which had remedial work done to them."

The commission will this afternoon hear evidence on remedial work done on the CTV building in 1991.

A 1990 report by engineering firm Holmes Consulting Group found the building might not be code-compliant.

Drag bars were installed on the top three levels to strengthen connections between the floor slabs and the north shear wall, allowing for greater stability in a quake.